I'm trying to figure out what is considered a power line( for outlets) and data communication line.
What are the qualifying factors here.
I know
outlets have 120V AC at 60Hz
and data lines have anything around 0 to 12V, but I don't know how much current that allows.

so

What is the current limit for the Data line?
What is the voltage limit for the Data line?

I would expect that results can vary based on where to you live.
I live in Utah, USA

2 Answers
2

National Electrical Code (Article 250.20 section A) defines "Low Voltage" as it applies to home distribution systems as less than 50 volts.

(A) AC Systems of Less Than 50 V. Alternating-current systems that
operate at less than 50 V are not required to be grounded unless:
(1) The primary exceeds 150 V to ground
(2) The primary is ungrounded

This includes systems such as cable television, network and telephone, doorbell, etc. Note that standard telephone wiring can typically "ring" at 48 volts and still provide an electric shock.

The reason the code makes the distinction for low voltage is so that some types of wiring can be exempt from additional safety requirements such as conduit usage, breakers, installation method, etc. Even so, there are still violations where installers confuse the issue (Top ten violations in low voltage systems PDF).

There are (to my knowledge) no current limits for data lines, except for the rating of the cable itself. Since most UTP network and telco cables use 24 or 26 gauge wire, this would theoretically be around 3.5 amperes, but you have to consider length, temperature, etc. to properly determine current load (discussion at allaboutcircuits).

EDIT

Guessing that you might be wanting to use data lines for higher power applications, I thought I'd add some additional commentary. If you are wanting to use Cat5 for power-over-ethernet applications, you'll probably want to stay under 1A or less per conductor. This is because of the voltage drop and resistance on longer distances. Keep in mind that higher voltages are more suitable for transmission (longer distances) as long as you stay under the 50V "low voltage" specification. Even though charts show that 24AWG can carry 3.5A, I wouldn't consider this safe unless working with a very short cable. Power-over-ethernet standards are confusing, but generally they are 48 volts or less at 600mA or less.

Electrical characteristics (at Wikipedia) for UTP Cat5E show a max current of 0.577A per conductor and a max voltage of 125V.

Thanks for the awesome answer. I am planning on using cat 5 but I plan on keeping the current below 0.5 per wire, and grouping 3 wires together. my voltage is at 24V and about 1.5 - 2 amps.
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AshitakalaxJul 3 '12 at 15:14

Article 250 as mentioned in the other answer does state that low voltage is 50 Volts or less, but it is in reference to grounding and bonding. The NEC does not define low voltage! You don't have to take my word for it, refer to Mike Holt. He is a well known expert on the NEC